<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>15-作业-发送短信</title>
</head>
<body>
    手机号码：<input type="number">
             <button>发送验证码</button>
    <script>
        /* 
            需求：
                1. 点击按钮 开启倒计时  按钮禁用
                2. 倒计时结束  按钮恢复
        */
       let btn = document.querySelector('button');
       btn.addEventListener('click',function(){
           let index = 3;
           this.disabled = true;
           btn.innerHTML = index;
           
           let timer = setInterval(() =>{
               index--;
               btn.innerHTML = index;
               if(index == 0){
                   clearInterval(timer);
                   this.disabled = false;
                   this.innerHTML = '发送验证码';
               }
           },1000);
       });
    </script>
</body>
</html>